The present invention relates to an apparatus for distributing fluid to a leach field in the practice of the art of hydrometallurgy.
The art of hydrometallurgy is described in some detail in U.S. Pat. No. 5,005,806, the disclosure of which is hereby incorporated herein by reference. In essence, hydrometallurgy is the art of recovering metals from ores by separating a solution of the metal in the form of a salt from the ore, then decomposing the metallic salt in such a way to cause precipitation of the metal from the solution. The leaching solution, or lixiviant, used depends on the particular metal being leached from the ore. For example, gold and silver are typically reclaimed from low grade ore using lixiviants generally constituting aqueous solutions of sodium cyanide mixed with oxygen to convert the metal to a soluble salt from which the metal can be recovered by precipitation. Leaching solutions of sulfuric acid or sulfuric acid-sulfate are typically used for leaching copper from an ore.
In the commercial practice of hydrometallurgy, a bed of run-of-mine or granular low grade ore, known as a heap, is spread over an impervious base or pad which may comprise sheets of plastic film, asphalt and/or compacted clay. Crushed ore is normally heaped onto the pad to a depth to 10 to 30 feet and leveled off at the top of the heap. The ore is typically pre-crushed to a desired size. For example, for copper mining, the ore may be crushed to one quarter inch granular size.
After the heap has been prepared, the target metal is leached from the ore by circulating the leaching solution through the heap in a process commonly known as percolation. To effect percolation, the solution is distributed over the top of the heap and permitted to seep down through the heap to the impervious pad. The impervious pad is typically sloped toward a drain pipe or channel for recovering the metal laden solution. The liquid that is distributed over the top of the heap may be a leaching solution comprising water mixed with a leaching agent, or a leaching agent may be premixed with the ore before the ore is spread onto the heap and relatively pure water is percolated through the heap. For example, in copper ore mining, sulfuric acid is mixed with one quarter inch crushed copper ore before the ore is spread onto the heap, and pure water is percolated through the heap to mix with the sulfuric acid and leach the copper from the ore.
Various systems have been used for distributing water over a leach field. For example, sprayers or sprinklers may be positioned at various locations on the heap to spray and distribute water or leaching solution over the top of the surface. Liquids distributed in such a manner are prone to rapid evaporation and degradation by exposure to air and ultra violet rays, and in addition, can be prone to freezing in cold weather operations. In addition, spraying techniques can result in surface puddling and run-off, raising the threat of channeling problems and potentials for blowouts.
U.S. Pat. No. 5,005,806 discloses a liquid distribution system which includes main line pipes extending longitudinally along a side of the heap and header pipes extending at spaced intervals from the main line pipe transversely across the heap generally parallel to one another. Extending in both directions across the heap from the header pipes are a plurality of generally parallel, closely spaced tubes. Liquid flows from the main line pipes, into the header pipes and into the tubes, and each tube has a plurality of spaced emitters secured thereon for directing the leaching solution onto the ore bed.
The general layout of a conventional copper ore leaching operation is shown in FIG. 1. The lay-out of the leach field 10 is generally that of an oval track having a first straight portion 12 a second straight portion 14 and first and second turning areas 20, 22. To make such an operation commercially viable, it is typically necessary that such a field be extremely large. For example, in commercial operations, each of the straight portion 12 and 14 may be up to 400 meters wide and 1.6 kilometers long, and the depth of the heap may be six meters.
In the leach field operation shown in FIG. 1, heaps are formed along the first and second straight portions 12 and 14 by a traveling stacker conveyor system 32, and spent ore is removed from the straight portions by traveling cleaner conveyer system 24. Copper laden ore mixed with sulfuric acid is brought into the field from a remote crusher and mixer along an underground inlet conveyer 16. The stacker conveyer assembly 32 branches off the inlet conveyer 16. Stacker conveyer system 32 includes a stacker conveyer 34 extending transversely across the straight portion 12 or 14 from the inlet conveyer 16. The stacker conveyer system 32 travels clockwise on the leach field shown in FIG. 1 supported on a plurality of endless track crawlers 36 which are typically powered by electrically powered hydraulic systems. A stacker mechanism (not shown) travels back and forth along the stacker conveyer 34 and distributes ore from the conveyer 34 onto the heap. The rate of movement of the stacker conveyer system 32 about the leach field 10 and the rate of movement of the stacker along the stacker conveyer 34 are preferably set so as to create a relatively evenly distributed heap of about 6 meters in depth. The heap is formed only on the straight portions 12 and 14 from the beginning 11 of straight portion 12 to the end 13 thereof and from the beginning 17 of straight portion 14 to the end 15 thereof.
In a conventional hydrometallurgy operation, such as that previously described, water is distributed to the heap to effect the leaching percolation in a manner similar to that disclosed in U.S. Pat. No. 5,005,806. That is, main pipes 40 and 38 bring fluid from a remote source to the leach field 10, a plurality of header pipes (not shown) extend transversely from the pipes 38 and 40 across the leach fields, and pluralities of closely spaced, generally parallel hoses (not shown) extend from the header pipes in both directions across the top of the heap. Rather than using specially designed emitters, however, the hoses are typically perforated at numerous locations along their respective lengths so as to allow fluid to leak therefrom onto the heap. The copper laden solution is directed by the impervious pad beneath the heap toward recovery pipes 42 and 44 which direct the solution to a facility at which the copper can be precipitated from the solution.
After the ore has been sufficiently leached, the spent ore is removed from the field by a traveling cleaner conveyer system 24. Cleaner conveyer system 24 comprises a conveyer 30 supported for clockwise translation about the leach field 10 on a plurality of endless track crawler mechanisms 28. A cleaner mechanism 26, typically comprising a rotary shovel device, travels up and down the cleaner conveyer 24, scooping spent ore from the heap onto the conveyer 30, which directs the spent ore towards the central underground conveyer and away from the leach field 10 through an outlet conveyer 18. Accordingly, as shown in FIG. 1, the area to the right of the cleaner conveyer system 24 is a cleaned area from which spent ore has been removed, and the area to the left of the conveyer system is a heap of spent ore or ore which is presently undergoing a percolation procedure.
It can be appreciated that the stacker conveyer system 32 and the cleaner conveyer system 24 follow each other about the leach field 10, the stacker conveyer system 32 distributing a heap of ore, and the cleaner conveyer system 24 removing the spent ore after percolation has been performed on the ore. The turning areas 20 and 22 are provided so as to permit the continuous forward translation of the stacker conveyer system 32 and cleaner conveyer system 24.
The previously described method of distributing water over the leach fields suffers from a number of disadvantages. The header pipes extending across the heaps from the main pipes 38 and 40 and the numerous perforated tubes extending from the header pipe across the heaps are typically assembled and disassembled using manual labor. The shear magnitude of the manual effort necessary to assemble and disassemble the fluid distribution systems can be appreciated when considering the overall size of the leach fields, typically 400 by 1600 meters in size. Accordingly, the assembly and disassembly of the fluid distribution system is incredibly labor and time intensive. In addition, the numerous tubes and pipes which must be manually assembled and disassembled are subject to damage and entanglement due to their frequent handling. Because the pipes and tubes are to be manually handled, they must necessarily be of light weight materials which makes them more susceptible to damage, especially in the rugged environment of a leach field operation. Also, because of the frequent connecting and disconnecting of the header pipes and the frequent connecting and disconnecting of the tubes to and from the header pipes, it is necessary that the connectors used be connectors capable of easy connecting and disconnecting. Such connectors are typically susceptible to wear and fatigue and therefore are prone to malfunction and require frequent replacement.